Throughout this application various publications are noted. The disclosures of these publications in their entireties are hereby incorporated by reference in this application in order to more fully describe the state of the art to which this invention pertains.
1. Field of the Invention
The present application discloses one or more inventions. The inventions relate generally to optical switching, and in particular, one invention relates to methods, devices and systems to optically switch a specific channel of light between optical fibers. Other inventions generally relate to the “on/off” switching of optical filters, which are specific for a signal in one wavelength or in one channel within a band of signals or band of channels, respectively.
2. Description of the Related Art
Dielectric microspheres are known in the art. It has been shown that a microsphere of the appropriate proportions can form a wavelength specific connection from one optical fiber to another by virtue of the dielectric microsphere's resonance in a whispering gallery mode (WGM) for the specific wavelength, or for a group of specific wavelengths of light which are the resonate frequencies. The WGM may be used to switch light transmission from one optical fiber to another. Depending on the placement of the microsphere and nature of the optical fibers, fairly high coupling efficiency and light transfer may be achieved. This is disclosed in “Highly Efficient Optical Power Transfer to Whispering Gallery Modes by Use of a Symmetrical Dual Coupling Configuration”, Ming, Cai and Kerry, Vahala, Opt. Lett 25, No. 4, 260 (2000).
Wavelength Division Multiplexing (WDM) is a technique which has been used to enhance the signal capacity of a single mode optical fiber by simultaneously transmitting multiple discreet wavelengths of light, referred to as “channels” in a single band. The wavelengths in each channel are separated by a pre-determined spacing, usually on the order of hundreds of GHZ. Dense Wavelength Division Multiplexing (DWDM) systems are characterized by closer spacing between the respective wavelengths comprising the channels thereby allowing for a greater number of channels within the same band in the same optical fiber as compared to WDM.
The speed of routing from one optical fiber to another is limited by the rate at which the optical switching occurs. In the past, switches which convert the optical data to electronic data have been a “bottleneck” in the system. Those acquainted with optical switching will recall that much interest has been shown in achieving the goal of a direct optical to optical switch which would eliminate the bottleneck caused by the optical to electronic conversions of the past. A variety of devices have been developed in pursuit of achieving this goal.
Common to many optical to optical switches and optical routers is an all or nothing functionality by which the entire signal, within a channel, is switched or not switched. While useful for small or local networks, especially those networks with easily controlled light sources (lasers), in larger or less controlled environments, an optical router must be able to accept signals from a variety of sources and seamlessly multiplex despite difference in the quality of the signals. Optical switches lacking the ability to monitor, equalize and/or groom the channels in nanoseconds or even picoseconds (which is “real time” for optical transmissions). This may yield turbidity within a band resulting in unbalanced light transmissions (signals) from channel to channel which in turn may cause noise, loss of part of a signal or channels to drop out.
Accordingly, applicants have identified a need for an optical switch and router that operate in “real time” (which is in the order of nanoseconds or picoseconds) for light transmission. Applicants have also identified a need for an optical router of “real time” optical switches which can monitor, groom, and/or balance a channel relative to the other channels in an optical band.
Further, with respect to the general field of dielectrics, it has been described by Grier & Dufresne in U.S. Pat. No. 6,055,106 that small dielectric particles may be contained in one or more optical traps. As stated above, optical trapping is known and can be used to contain and manipulate small particles in the submicron to hundreds of micron range.
Depending on the placement of a WGM microsphere, the nature of the optical fibers, and the diameter or taper of the optical fibers, high efficiency of light transfer may be achieved for the resonate frequencies. See, “Highly efficient optical power transfer to whispering-gallery modes by use of a symmetrical dual coupling configuration”, Ming Cai and Kerry Vahala Opt. LETT 25, No. 4, 260 (2000); “Phase-matched excitation of whispering-gallery-mode resonances by a fiber taper”, J. C. Knight, G. Cheung F. Jacques, and T. A. Berks, Opt. LETT 22, No. 15, 1129 (1997). Particular attention should be paid to FIG. 2, and “Time-domain observation of optical pulse propagation in whispering-gallery modes of glass spheres”, R. W. Shaw, W. B. Whitten, M. D. Barnes, and J. M. Ramsey, Opt. LETT. 23, No. 16, 1301 (1998).
In determining Q for a silica microsphere, physical factors which reduce Q below the limit defined by material losses Q−1mat are the losses attributable to Q−1cont, Q−1rad and Q−1s.s. Wherein Q−1cont are those losses due to surface contaminants, Q−1rad are those losses attributable to the smallness of the diameter of the microsphere and Qss represents losses due to scattering caused by surface imperfections. Measurements of losses indicate that if the diameter of a microsphere divided by the wavelength of light it was resonating for is ≧15 then Q−1rad is >1011. Additionally, for microspheres larger than 100 microns in diameter Q−1s.s is <<1×10−10. “Ultimate Q of optical microsphere resonators” M. L. Gorodetsky, A. A. Savchenkov, and V. S. Ilchenko Opt. LETT 21, No. 7, 453-455.
It has been described by Knight that a microsphere coupled to an optical fiber with a stripped off polymer coating (cladding) over a region of the optical fiber, which has been drawn out in a tapered waist region, can achieve high coupling efficiency in the waist region. Coupling is to the evanescent tail of a signal, extending out into the free space along the region of the optical fiber surrounding the taper. Knight reported a coupling efficiency of a microsphere resonator at a tapered waist region with measurements of Q as high as 5*107.
One method to taper an optical fiber is to apply heat to an optical fiber and cladding above their respective melting temperatures so that it will stretch, and apply a stretching force. U.S. Pat. No. 5,729,643 issued to Hmelar.
With respect to WDM, as stated above, the wavelengths in each channel are separated by a pre-determined spacing usually in the order of hundreds of GHz and with transmission rates up to about 10 Gb/s. DWDM systems are characterized by closer spacing in the order of 50 to 12.5 GHz between the respective channels. The closer spacing allows for a greater number of channels within the same band in the same waveguide as compared to WDM, for example 320 DWDM channels at 10 Gb/s yields a 3200 Gb/s fiber capacity as compared to 80 channels at 10 Gb/s which yields an 800 Gb/s fiber capacity.
In addition to WDM and DWDM, optical networks may increase fiber capacity with time division multiplexing (TDM). TDM can achieve a 3200 Gb/s fiber capacity by combining less channels and faster transmission rates. For example, 80 channels at 40 Gb/s yields the 3200 Gb/s fiber capacity and maintains greater channel spacing by reducing the Bit periods. However, reduction of the Bit period from 10 Gb/s to 40 Gb/s reduces the window through which to measure waveform from 100 picoseconds to leave only a 25 picosecond window. Photonics Spectra September 2001, “Faster vs. Denser: Networks Reach Another Crossroads”, by Daniel C. McCarthy. Therefore, in WDM, DWDM or TDM optical networks picoseconds switching is “optical real time”.
Accordingly, there exists a need for an optical filter which has the ability to select and switch at least one specific wavelength light signal from among a group of wavelength light signals within an optical transmission band in “optical real time”; and which can filter out in “optical real time” specific wavelength light signals, from among all the different wavelength light signals which may be found within the channels of an optical transmission band.